Exhaust duct for an electron tube



6, 195,7 4 A. L. STURGES 2,802,134

EXHAUST DUCT FOR AN ELECTRON TUBE Filed May 7, 1954 INVENTOR. ALBERT L. STURGES ATTORNEY United States Patent 9 EXHAUST poor FOR AN ELECTRON TUBE Albert L. Sturges, Springdale, Conn., assignor to Machlett Laboratories Incorporated, Springdale, Conm, a corporation of Connecticut Application May 7, 1954, Serial No. 428,281

1 Claim. (Cl. 313326) This invention relates to exhaust ducts for electron tubes. More specifically, this invention relates to exhaust ducts which are designed to penetrate the anode surface in an electron tube structure where that active surface is composed of a sheet metallic member backed by a conductive block member.

In Patent No. 2,667,593 to Howard D. Doolittle, a novel duct designed to penetrate the active anode surface is described and claimed in combination with an expansion compensation structure. Independent of the expansion compensation aspects of the invention, this novel duct has advantages, the most obvious advantage being greater ease of manufacture. This invention is an improvement over the exhaust duct of the Doolittle invention. However, it is not limited to use with expansion compensating structures, and, accordingly, it is somewhat broader in scope than the Doolittle application over the narrow range of its coverage.

In manufacturing electron tubes it is desirable to make as many of the necessary brazed joints as possible at one time. It is desirable to make many joints at one time because each brazing operation requires the care of a skilled craftsman and takes a relatively long period to complete. Moreover, it is desirable to minimize the number of brazing operations because of the necessity on subsequent operations to avoid melting of, or other deleterious effects to, the previously made brazed joints. It is necessary, in order to avoid harm to the previously made joints, to accomplish subsequent brazing at a temperature lower than that at which the previously used solders will melt. This means that a plurality of solders must be employed and the first brazing must be carried on at much higher temperatures than the last. If a multiplicity of brazing operations are required, unusual and expensive solders may be required, and it may be necessary in order to melt these various solders, to bring the heating on subsequent cycles dangerously close to the temperature which will effect adversely previously made joints.

In structures employing a highly conductive metallic block behind a sheet metallic active anode surface, it is frequently standard production practice to complete both the brazing of the sheet metallic member to the block and the exhaust tubulation to the block in the same operation. Inasmuch as the exhaust duct is drilled through the anode structure before the exhaust tubulation is put into place, it has become a serious problem in the brazing operation to avoid the overflow of excess solder into the exhaust duct. Such overflow has necessitated redrilling the exhaust duct and has been the cause of considerable nuisance and disadvantage. Moreover, sometime particles from the drilling operation will wedge themselves between the block and the sheet metallic anode surface. Certain impurities, which are carried along with these particles, later may adversely affect the tubes qualities when the anode structure becomes heated during tube operation.

It is the object of this invention to avoid this necessity for redrilling the axial exhaust duct. It is also the object of this invention to avoid any occlusion of metallic or other foreign particles which may adversely affect the tubes vacuum quality and electrical operation. The expedient for avoiding these difficulties is the use of a tubulation which extends clear through the anode block and terminates at the active anode surface with the end of the tubulation coinciding with the active anode surface. With this construction it is possible to complete the brazing of both the block to the active sheet metallic anode member and the tubulation to the block without any danger of overflow of solder into the duct or the problem of later contamination.

For a better understanding of this invention reference is made to the drawing which illustrates in partial section the novel exhaust structure of the present invention.

Referring to the drawing the tube illustrated is a conventional coaxial tube structure commonly known to the art as an inverted lighthouse tube structure. In this structure coaxial terminals 10 and 11, which are mutually insulated from one another, respectively support the cathode and grid electrodes within the vacuum envelope. The grid is supported on the support structure generally designated 12 which extends in close proximity to the active anode surface 13. All of the electrodes in this tube structure are planar. A grid terminal 11 which serves as a portion of the vacuum envelope is joined by dielectric ring 16 to anode terminal 15 which is a tubular member, and also a portion of the vacuum envelope. Within anode terminal 15, and soldered vacuum-tight thereto, is cup member 17 which is advantageously composed of a material which compensates for the expansion of envelope members, 11, 16 and 15, and grid support structure 12, so that the grid-anode spacing is maintained essentially constant. The active anode surface is the bottom surface of cup 17. Within the cup, but outside the vacuum envelope, is a block 18 of highly conductive material, such as copper. To this block may be attached, for example, a radiator for air-cooling the anode. The highly conductive material quickly carries the heat generated at the anode surface away from the surface and permits cooling which avoids destruction of the anode. The smaller end of the anode block 18 snugly fits within the portion of cup 17 adjacent the active surface of the anode and is advantageously brazed thereto in a vacuumtight seal at joint 19, which joint extends under anode face 13 and around tubulation 20. Overflow of the solder is collected in annular groove 19a. A copper exhaust tubulation 20 is made to extend all the way through anode block 18 and the bottom of cup 17. The end of tube 20 coincides with active anode surface 13. Certainly, the tubulation must extend beyond the junction of block 18 and cap 17 to be effective. Tube 20 and anode block 13 are brazed together, as is illustrated at joint 21.

After the vacuum envelope has been exhausted, if the tubulation is copper, it may be sealed-off vacuum-tight by pinching together its side walls using pliers having rounded jaws. This operation will effect a cold welded vacuum-tight seal.

The present invention is not confined to use with coaxial tube structures such as that shown. In fact, it may be used with any tube structure wherein the active anode is composed of a sheet metal member backed by a highly conductive backing material, which functions. either to transmit or store heat generated at the active anode surface. The many uses and variations in the 'present invention will occur to one skilled in the art, and,

within the scope of the claim, they are intended to be. within the scope and spirit of the present invention.

I claim:

An electron tube comprising an anode structure embodying a cupped active anode, an anode block located within and secured to the base portion of the cupped ac tive anode, the anode block having an axial opening there through and the active anode having an aperture in the base thereof, which aperture is coaxial with and of the same diameter as the opening in the, anode block, the opening and aperture forming an axial duct having smooth unbroken inner walls of a single diameter throughout and extending from the exposed surface of the active anode to the exposed outer surface of the anode block, and an exhaust tubulation comprising a metal tube relatively permanently sealed within the duct in vacuum-tight relation to the walls thereof, and in relatively intimate engagement throughout its circumference with the walls of said aperture, the tube sealing the joint between the active a 4 4 anode and the anode block and having one end surface thereof aligned substantially in the plane of the exposed surface of the active anode and having its opposed end extending outwardly of the exposed outer surface of the anode block.

References Cited in the file of this patent UNITED STATES PATENTS 2,277,440 Knochel Mar. 24, 1942 2,424,805 De Walt July 29, 1947 2,667,593 Doolittle Jan. 26, 1954 

